An anti-government protester is engulfed in flames during clashes with riot police outside Ukraine's parliament in Kiev, Ukraine, Tuesday, Feb. 18, 2014. Thousands of angry anti-government protesters clashed with police in a new eruption of violence following new maneuvering by Russia and the European Union to gain influence over this former Soviet republic. (AP Photo/Efrem Lukatsky) less

TOPSHOTS Anti-government demonstrators stand on barricades during clashes with riot police in Kiev on February 18, 2014. Opposition leader Vitali Klitschko on February 18 urged women and children to leave the opposition's main protest camp on Kiev's Independence Square, known as Maidan, as riot police massed nearby. "We ask women and children to quit Maidan as we cannot rule out the possibility that they will storm (the camp)," the former heavyweight boxing champion told protestors on the square. AFP PHOTO / SANDRO MADDALENASANDRO MADDALENA/AFP/Getty Images less

TOPSHOTS Anti-government demonstrators stand on barricades during clashes with riot police in Kiev on February 18, 2014. Opposition leader Vitali Klitschko on February 18 urged women and children to leave the ... more

Photo: Sandro Maddalena, AFP/Getty Images

Police move in against Ukraine protest camp

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KIEV, Ukraine -- - Amid cries of "Glory to Ukraine!" and with flaming tires lighting up the night sky, thousands of riot police armed with stun grenades and water cannons attacked the sprawling protest camp in the center of Kiev on Tuesday, following a day of street battles that left 18 people dead and hundreds injured.

The violence was the deadliest in nearly three months of antigovernment protests that have paralyzed Ukraine's capital in a struggle over the nation's identity, and the worst in the country's post-Soviet history.

With the boom of exploding stun grenades and fireworks nearly drowning out his words at times, opposition leader Vitali Klitschko urged the 20,000 protesters to defend the camp on Independence Square that has been the heart of the protests.

"We will not go anywhere from here," Klitschko told the crowd, speaking from a stage in the square as tents and tires burned around him, releasing huge plumes of smoke. "This is an island of freedom and we will defend it," he said.

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Many heeded his call.

"This looks like a war against one's own people," said Dmytro Shulko, 35, who was heading toward the camp armed with a fire bomb. "But we will defend ourselves."

As police dismantled some of the barricades on the perimeter of the square and tried to push away the protesters, they fought back with rocks, bats and fire bombs. Many of the protesters were bleeding.

Speaking over loudspeakers, police urged women and children to leave the square because an "antiterrorist" operation was under way.

The protesters appeared to sense that Ukraine's political standoff was reaching a critical turning point. As the tents and also some tires went up in flames, defiant protesters shouted "Glory to Ukraine!" and sang the Ukrainian national anthem.

Shortly before midnight, Klitschko headed to President Viktor Yanukovych's office to try to resolve the crisis, his spokeswoman said. An hour later, he was still waiting to be received.

Earlier in the day, protesters attacked police lines and set fires outside parliament, accusing Yanukovych of once again ignoring their demands and dragging his feet on a constitutional reform to limit presidential powers.

Tensions had soared after Russia said Monday that it was ready to resume providing the loans that Yanukovych's government needs to keep Ukraine's ailing economy afloat. This raised fears among the opposition that Yanukovych had made a deal with Moscow to stand firm against the protesters and would choose a Russian-leaning loyalist to be his new prime minister.

The protests began in late November after Yanukovych turned away from a long-anticipated deal with the European Union in exchange for a $15 billion bailout from Russia.

Until Monday, the two sides had appeared to be making some progress toward resolving the political crisis peacefully.

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